The present invention relates to a multilayer printed board, and more particularly to a multilayer printed board with a double plane spiral interconnection structure for suppressing electromagnetic interference.
The multilayer printed board has a power source layer and a ground layer. A high frequency current flows through the power source layer to operate integrated circuits or large scale integrated circuits. It is necessary to prevent the high frequency current from so flowing as to draw a large current loop between the power source layer and the ground layer. In Japanese laid-open patent publication No. 9-139573, it is disclosed to emphasize the power de-coupling, wherein the power source layer has interconnections which include an impedance-circuit in the form of zigzag, winding crossing or spiral for forming an impedance, and also insulation layers sandwiching the power source layer are made of an insulator mixed with a magnetic material.
The conventional multilayer printed board has the following two problems.
The first problem is that when the IC or LSI mounted on the multilayer printed board operates, a high frequency current flows from the IC or LSI to the power source layer, whereby a power system comprising the power source layer and the ground layer allows a large current loop serving as a looped antenna from which electromagnetic waves as noises are radiated.
The second problem is that in switching IC or LSI, a current from the power source layer to the IC or LSI causes a voltage variation the power source layer. This voltage variation causes a stationary wave in the power system serving as a looped antenna from which electromagnetic waves as noises are radiated.
In the above circumstances, it had been required to develop a novel multilayer printed board free from the above problem.